I CHARACTERS OF THE NUCLEUS 7 



unless special means are taken to preserve it, undergo more 

 or less speedy decomposition. 



Many of these properties of protoplasm can hardly be 

 verified in the case of Amoeba, owing to its minute size and 

 the difficulty of isolating it from other organisms (water- 

 weeds, &c.) with which it is always associated; but there 

 are sope tests which can be readily applied to it while 

 under observation beneath the microscope. 



One of the most striking of these micro chemical tests 

 depends upon the avidity with which protoplasm takes up 

 certain colouring matters. If a drop of a neutral or slightly 

 alkaline solution of carmine or logwood, or of some aniline 

 dye, or a weak solution of iodine, is added to the water con-' 

 taining Amoeba, the animalcule is killed, and at the same 

 time becomes more or less deeply stained. 



The staining is, however, not uniform. The endosarc, 

 owing to the granules it contains, api)ears darker than the 

 ectosarc, and there is usually to be seen, in the endosarc, a 

 rounded spot more brightly stained than the rest. This 

 structure, which can sometimes be seen in the living Amoeba 

 (Fig. I, c, E, and g, nu), while frequently its presence is 

 revealed only by staining (comp. a and b), is called the 

 nucleus. 



But when viewed under a sufficiently high power, the 

 nucleus itself is seen to be unequally stained. It has lately 

 been shown, in many Amoebae, to be a globular body, en- 

 closed in a very delicate membrane, and made up of two 

 constituents, one of which is deeply stained by colouring 

 . matters, and is hence called chromatin, while the other, the 

 nuclear sap or achromatin, takes a lighter tint (Fig. I, y). 

 The relative arrangement of chromatin and sap varies 

 in different Amoebae : sometimes there are granules of 

 chromatin in an achromatic ground substance (f); some- 



